Preparation of 1, 2, 4, 5-tetrallkylbenzenes from pseudocumene and propylene



' alkylbenzenes formed, while (durene), formed by transmethylation during the alkyla- United States Patent 3,132,189 PREPARATEON 0F 1,2,4,5 TETRAALKYL- BENZENES FROM PSEUDOCUMENE AND PROPYLENE 1 Eugene F. Lutz, Denver, Colo., assignor to Marathon Oil Company, Findlay, Ohio, a corporation of Ohio No Drawing- Filed July 17, 161, Ser. No. 124,320 '2 Claims. (Cl. 260-671) 1 t This invention relates to .a process for the selective synthesis of 1,2,4,5-tetraalkylbenzenes in the presence of a moist aluminum chloride catalyst. More specifically, this invention relates to the-preparation of l-isopropyl-Z, 4,5 trimethylbenzene and 1,2,4,5 tetramethylbenzene (durene) as the predominant products from the alkylation of pseudocumene with propylene in the presence of a moist aluminum chloride catalyst.

1,2,4,5-tetraalkylbenzenes are of interest as intermediates for the preparation of pyromellitic dianhydride, a valuable chemical in the synthesis of numerous plasticizers, resins, and polymeric films. The 1,2,4,5-tetraalkylbenzenes may be oxidized by nitric acid and other common oxidizing agents to the corresponding tetrabasic acid which can readily be converted to pyromellitic dianhydride.

According to the present invention 1 have discovered that pseudocumene may be alkylated with propylene in the presence of a moist aluminum chloride catalyst to produce an alkylate whose composition is at least 60% 1,2,4,5 tetraalkylbenzenes. 1-isopropyl-2,4,5-trimethylbenzene accounts for about 43-54% of the 1,2,4,5-tetra- 1,2,4,5-tetramethylbenzene tion reaction, accounts for about 5-15 of the 1,2,4,5-

tetraalkylbenzenes. Both durene and 1-isopropyl-2,4,5- trimethylbenzene are readily converted to pyromellitic dianhydride.

Included among the objects and advantages of the present invention is a process for the selective production of 1,2,4,5-tetraalkylbenzenes by the alkylation of pseudocumene with propylene in the presence of a moist aluminum chloride catalyst. The process provides an alkylation catalyst which will selectively produce 1,2,4,5-'

" tetraalkylbenzenes in relatively high yield. This process provides an inexpensive and highly eflicient method for producing certain intermediates and useful compositions by alkylating an inexpensive and readily available petroleum product.

A primary advantage of this process over those already known is'in the selectivity with which inexpensive petrochemicals may be converted to 1,2,4,5-tetraalkylbenzenes in high yield. D. A. McCaulay has shown in US. Patents No. 2,803,681 and 2,848,511 that when tetramethylbenzenes are synthesized by the disproportionation of trimethylbenzenes, such as pseudocumene, in the presence of an ordinary Friedel-Crafts catalyst, low conversion yields 10-30%) must be taken in order to maintain a reasonably high percentage of 1,2,4,5-tetramethylbenzene v (durene) in the product mixture of tetramethylbenzenes. When higher conversion yields are taken, an equilibrium mixture of tetramethylbenzenes is obtained which has approximately the following composition: 50% isodurene (1,2,3,5-tetramethylbenzene), 45% durene (1,2,4,5-tetramethylbenzene) and a 5% prehnitene (l,2,3,4-tetramethylbenzene). This work clearly illustrates the difiiculty involved in trying to prepare a 1,2,4,5-tetramethylbenzene in high yield in the presence of an ordinary Friedel- Crafts catalyst.

Still other patents report the alkylation of pseudocumene with such relatively expensive alkylating agents as methanol and methyl chloride, for example US. Patent No. 2,945,899.

3,132,189 Patented May 5, 1964 To about 12 grams (0.1) of pseudocumene was added about 1.4 grams of aluminum trichloride and about 0.5 gram of water in a three-necked flask, equipped with a condenser, thermometer, stirrer, and gas bubbler. The mixture was heated to about -90 C. and after reach ing that temperature propylene gas was passed into the solution at a rate of about 37 cc. per minute. The course of the reaction was followed by gas-liquid chromatographic analysis of small aliquots of the reaction mixture taken at regular intervals. After a period of about two hours the reaction was terminated, the reaction mixture was cooled, and the catalyst removed by filtration. Gasliquid chromatographic analysis showed that one compound accounted for about 84% of the reaction mixture. Distillation through a glass helices packed column gave the following fractions:

n =l.5209, 1st=68-l00i C./19 mm. (0.6 g.) n =1.5048, 2nd=100-104 C./19 mm. (1.4 g.) n =1.5O43, 3rd=104l08 C./19 mm. (7.4 g.) n =1.5111, residue=clear liquid (3.3g)

Due to the closeness of the boiling'point, the second and third cuts were considered essentially pure I-isopropyl-2,4,5-trimethylbenzene obtained in a yield of about 54.3%. The structure of the product was established by ultraviolet, infrared and nuclear magnetic resonance spectra. In addition the molecular weight and physical constants checked with the known values of the compound, 1-isopropyl-2,4,5-trimetl1ylbenzene.

Example 11 Following the procedure of Example I about 96 grams of pseudocumene, about 11.2 grams of aluminum trichloride and about 4 grams of in a vessel and heated to 85-90 C., after which propylene was bubbled into the reaction mixture at a rate of about 60 cc. per minute. The reaction was carried out Example III Following the above procedure, about 48 grams of pseudocumene, about 5.6 grams of aluminum trichloride and about 2 grams of distilled water were heated to a temperature of 8590 C. and after establishing the reaction temperature, propylene was bubbled into the reaction mixture at a rate of about 60-85 cc. per minute. The reaction was carried out for a period of about three and a half hours after which time the mixture was cooled and filtered. The reaction solution weighed about 64.4 grams whereas the expected weight if all the reactivants were converted to the tetraalkylbenzene would be 64.8 grams. 7 i

The reaction of the invention may be carried out at temperatures generally below the boiling point of pseudistilled water were placed 1 documene and generally in the range of 70-150" C. It is mixed 1,2,4,S-tetraalkylbenzenes which comprises heating pseudocumene with propylene in the presence of a catalytic amount of moist aluminum trichloride for a period of from one to five hours and in a temperature range of about 80-90 C., and then separating from the reaction mixture a mixture of 1-isopropyl-2,4,5-trimethylbenzene and 1,2,4,5-tetramethylbenzene.

2. A process for the preparation of a high yield of 1- isopropyl-2,4,S-trimethylbenzene which comprises heating pseudocumene in the presence of a catalytic amount of moist aluminum trichloride in a temperature range of from about 70150 C., and bubbling propylene through the heated mixture for a period of from one to five hours, and then separating from the reaction mixture a mixture containing a major portion of l-isopropyl-2,4,5,-trirnethylbenzene and a minor portion of 1,2,4, S-tetramethylbenzenei.

References Citedin the file of'this patent V UNITED STATES PATENTS 2,740,819 Kirkland .Apr. 3, 1956 2,882,324

Schmerling Apr. 14, 1959 

1. A PROCESS FOR THE PREPARATION OF AHIGH YIELD OF MIXED 1,2,4,5-TETRAALKYLBENZENES WHICH COMPRISES HEATING PSEUDOCUMENE WITH PROPYLENE IN THE PRESENCE OF A CATALYTIC AMOUNT OF MOIST ALUMINUM TRICHLORIDE FOR A PERIOD OF FROM ONE TO FIVE HOURS AND IN A TEMPERATURE RANGE OF ABOUT 80-90*C., AND THEN SEPARATING FROM THE REACTION MIXTURE A MIXTURE OF 1-ISOPROPYL-2,4,5-TRIMETHYLBENZENE AND 1,2,4,5-TETRAMETHYLBENZENE. 